The phenotypic characteristics of 48 isolates obtained from root nodules of four Acacia species (Acacia cyanophylla, A. gummifera, A. horrida and A. raddiana) growing in soils collected from the arid and Saharan regions of Morocco were studied. The rhizobia were very diverse with respect to their cross-nodulation patterns, as well as their physiological and biochemical properties. Dendrograms obtained through computer numerical analysis of 52 phenotypic characteristics showed that isolates could fit into four clusters below the boundary level of 0·85 average distance and that they were very distinct from the reference strains. Some interesting isolates for inoculation trials have been identified. They were able to grow at pH ranging from 4 to 9, tolerate a high salt concentration (3% NaCl) and grew at a maximum temperature between 35 and 40 °C.